During the last 10 to 20 years, the methodologies employed for treating recirculating cooling tower systems have changed dramatically. Previous widely used methods for corrosion and deposit control involved the use of chromate based inhibitors plus an acid for scale control and not too much use of dispersants or antifoulants. The pH of the recirculating water was typically acidic and occasionally as high as neutral and the hardness of the water was relatively low due to the nature of the treatment and the few cycles of concentration (e.g., about 3). Such conditions resulted in comparatively low bioburden and biofouling. Good microbiological control was typically achieved by use of chlorine alone or in conjunction with certain nonoxidizing biocides to supplement the chlorine.
In more recent times the problem of biofouling of cooling tower systems has become much more severe due to the dramatic change in water treatment methodology. Nonchromate and chromate based on higher pH's are used as well as extensive use of dispersants. The pH of the recirculating water is much more alkaline and the hardness of the recirculating water has also increased due to the nature of the newer treatment and the substantially higher cycles of concentration typically employed (e.g., about 6-10).
The increase in the pH and hardness of the recirculating water has substantially reduced the effectiveness of chlorine and certain non-oxidizing biocides for controlling biofouling.
In addition, it is well known in the art that even subtle changes in a given environment can have a profound impact on the quality and quantity of any microflora present. Moreover, it is also well known that continuous use of a biocide will result in selections of organisms resistant to the biocide which can lead to ineffectiveness of that biocide over time.
For the above-noted reasons, it would be greatly desired to have a commercially acceptable method for controlling biofouling employing a biocide which is effective in inhibiting microorganisms at an alkaline pH and/or at high water hardness.